Nowadays, electronic products developed by many manufacturers have a built-in camera module in order to attract consumers. Unfortunately, photoelectronic components equipped in many camera modules are not of good quality, so when they are used by users to take a photograph in poor lighting conditions, the generated image usually presents a very low contrast ratio. To process an image with a low contrast ratio, post-processing technologies have been adopted by many people. Among such post-processing technologies, the most commonly adopted one is the histogram equalization processing technology, which scatters intensity values of the image.
FIG. 1A depicts an image with a low contrast ratio, while FIG. 1B depicts a histogram of the image of FIG. 1A. FIG. 1C depicts an image obtained by processing the image of FIG. 1A through histogram equalization, while FIG. 1D depicts a histogram obtained by processing the histogram of FIG. 1B through equalization. As can be seen from FIG. 1C and FIG. 1D, although the image presents a higher contrast ratio after being applied histogram equalization, a phenomenon of histogram quantization (i.e., discontinuity of intensities) is caused.
In fact, in addition to images processed through histogram quantization, the problem of quantization may also occur to histograms of some images that haven't been post-processed. Therefore, efforts still have to be made in the art to solve this problem.